To me, pain differs from suffering. Pain is of the body and suffering is of the mind.
But I think your point still stands. There are plenty of reasons to purposefully subject yourself to pain (e.g. exercise).
I'm not sure about suffering. Suffering is an unavoidable side-effect of love and other delights of life, but it doesn't seem like something to ever be sought after. I'll need to think on that some more.
Also, your "when should" trick is clever! Good strategy for keeping things concrete.